The average age for a woman to have her first child has been increasing for the last three decades in the United States, making our understanding of ovarian aging and its negative effect on the ovarian reserve?a measure of the capacity of the ovary to produce eggs capable of fertilization?increasingly important. Yet, we know very little about other factors in reproductive-age women that might affect the ovarian reserve, beyond aging itself. This proposal, titled Study of Ovarian Aging and Reserve in Young Women (SOAR), seeks to address the significant gap in our knowledge of factors?particularly modifiable factors?that affect ovarian reserve and might accelerate its decrease in young women. To achieve this goal, we will leverage the ongoing NIEHS Study of Environment, Lifestyle and Fibroids (SELF), which is following a cohort of 1,696 African- American women between the ages of 23-34 years over a five-year period. In this group of young women, we will assess changes in the ovarian reserve by tracking three different measures of the ovarian reserve: anti- Mllerian hormone (AMH), early follicular phase follicle-stimulating hormone (FSH), and antral follicle count (AFC). In addition to collecting survey data, we will also perform oral glucose tolerance testing (OGTT) and anthropometric and bioelectrical impedance analysis (BIA) measurements to more precisely determine the roles of glucose metabolism and obesity on the ovarian reserve. The results of our study will be clinically significant as we currently have limited longitudinal data for counseling women on risk factors for decreased ovarian reserve. Our study design is innovative in that we will use overlapping measures of the ovarian reserve and group-based trajectory modeling to determine correlates associated with decreased ovarian reserve. Specifically, we will determine the demographic, health-behavior, reproductive, and environmental factors associated with decreased AMH (as a measure of the ovarian reserve) over time (Aim 1), determine the association between various measures of obesity and decreased ovarian reserve (Aim 2), and determine the association between glucose dysregulation and decreased ovarian reserve (Aim 3). The proposed prospective longitudinal cohort study will determine the natural history of and factors associated with the change in ovarian reserve over time. Further, it will add to the extremely limited data by generating the largest set of longitudinal data on AMH and ovarian reserve in the United States to date, which will benefit all women.